* Start the ISO format flags at bit 0 instead of bit 1.
* Remove unnecessary _8601 from ISO format flag names to
avoid line wrapping and to ease readability.
* ISO timestamps have date-time-timzone in common, so move
the TIMEZONE flag to bit 2 causing all timestamp masks
to have the first three bits set and the last four bits
as timestamp 'options'.
* Change the 'SPACE' flag to a 'T' flag, because it makes
the code and comments more concise.
* Add common ISO timestamp masks.
* Implement the ISO timestamp masks in all applicable code
using the strxxx_iso() functions.
Signed-off-by: J William Piggott <elseifthen@gmx.com>